Re: Performance Regression in Linux Kernel 5.19

[Peter Zijlstra]

On Fri, Sep 09, 2022 at 11:46:08AM +0000, Manikandan Jagatheesan wrote:
> As part of VMware's performance regression testing for Linux
> Kernel upstream releases, we have evaluated the performance
> of Linux kernel 5.19 against the 5.18 release and we have 
> noticed performance regressions in Linux VMs on ESXi as shown 
> below.
> - Compute(up to -70%)
> - Networking(up to -30%)
> - Storage(up to -13%) 
>  
> After performing the bisect between kernel 5.18 and 5.19, we 
> identified the root cause to be the enablement of IBRS mitigation 
> for spectre_v2 vulnerability by commit 6ad0ad2bf8a6 ("x86/bugs: 
> Report Intel retbleed vulnerability").
>  
> To confirm this, we have disabled the above security mitigation
> through kernel boot parameter(spectre_v2=off) in 5.19 and re-ran
> our tests & confirmed that the performance was on-par with 
> 5.18 release. 

Well, duh.. :-)